Resist materials are used in the formation of printed circuits, exposure masks and micro electronic devices. The resists are light or high energy radiation sensitive organic polymer materials which form an image pattern upon exposure and development. Negative resists become insolubilized or cross-linked in the exposed areas so that development removes the unexposed portions of the resist layer. Positive resists, on the other hand, are degraded in the energy struck areas so that the exposed portions are removed by the developer and the unexposed resist remains. The resist pattern is resistant to various physical and chemical processes so that the substrate, upon which it is formed, is protected in the areas which are masked by the resist.
The final step in the resist process, after the pattern has fulfilled its masking function, is resist removal or stripping. Because the resist layers are often post hardened to improve their masking characteristics and their adherence to the substrate, or are hardened by the process to which the substrate is subjected, the removal of the resist without leaving a residue, is sometimes difficult. Methods which have been used to strip resist layers include abrasion, plasma ashing in oxygen, and solvent and/or chemical action. The first two methods can be detrimental to certain substrates, such as thin layer metallurgy, by abrading or oxidizing them. Commonly used solvent or chemical strippers may also chemically degrade the substrate and/or may be difficult to completely remove from the substrate following the stripping process. Some of the stripping solutions contain halogenated hydrocarbons or phenols. These materials are unsatisfactory for certain applications in that free halogens which are released by the halogenated hydrocarbons will attack metals such as copper, nickel and iron so that the presence of stripper residues, which are entraped on the substrate, can cause latent attack and reliability problems. Both halogenated hydrocarbons and phenols present handling and disposal problems from an environmental standpoint.
A stripping process has now been found which employs a stripping solution which is halogen free, which can remove either positive or negative resist layers, and which requires only an alcohol or water rinse to completely remove the solution from the substrate.